In dental practice the professional uses impression materials to obtain impressions of teeth which are then used to mold caps, crowns and inlays, or other prosthesis. Precision of impression molds is a paramount consideration for comfort of the prosthesis. Realizing precision of impression is dependent on obtaining a good impression in the first place, and maintaining the good impression and this requires high gel strength and tensile strength in the gelled impression composition during removal from the teeth and through use in the forming the plaster from which the prosthesis is to be made.
Many dentists prefer the use of reversible hydrocolloid gels as impression compositions which are unparalled for accuracy. These gels are obtained by mixing water and a gel base such as agar-agar, and tempering the gel in a conditioning bath until used.
The following patents relate to reversible hydrocolloid gel impression materials, and have been considered in preparing this application: U.S. Pat. No. 2,021,059 to Harrison; U.S. Pat. No. 2,089,552 to Harrison; and, U.S. Pat. No. 2,234,583 to Preble. The first two of these patents teach the use of glycerol in hydrocolloid compositions, but such systems require a higher temperature tempering bath to avoid loss of workability, and thus a pre-application conditioning step, while the last of these patents teaches that an increase in strength of reversible hydrocolloid gel materials is realized by the use of borates, but such systems as are taught are grainy, lumpy, and too viscous for utility as impression materials.